Sarcoidosis is a disease of unknown etiology, characterized pathologically by noncaseating granulomas which most commonly involve the lung, skin, lymph node and eyes. Syndromes with similar pathologic and immunologic features to sarcoidosis such as chronic beryllium disease, hypersensitivity pneumonitis, and tuberculosis illustrate that granulomatous diseases may or may have an infectious etiology. We performed PCR analysis of paraffin-embedded sarcoidosis and control specimens for the presence of Mycobacterium 16S rRNA and rpoB. We found evidence of mycobacterial nucleic acids in 60% of the sarcoid granulomas and in none of the controls (p<0.00002, chi square). Sequence analysis of the 16S rRNA and rpoB amplicons revealed the presence of a novel Mycobacterium, genetically similar to M. tuberculosis (MTB) (99% positional identity). We expanded our work to include ten frozen sarcoidosis and ten control tissues from Vanderbilt University and from other regions of the United States. We identified mycobacterial nucleic acid in 50% of frozen sarcoidosis specimens and in none of controls (p<0.0325, two-tailed Fisher's test). Most recently, we performed ELISPOT assays on sarcoidosis '(n=10) and control (n=9) peripheral blood mononuclear cells (PBMC). We found immune recognition of MTB katG peptides in 70.0% of the sarcoidosis specimens compared to none of the negative control specimens (p=0.01, ANOVA analysis). The central hypothesis is that sarcoidosis is an immunologic response to a mycobacterial infection in a genetically susceptible host. We have formed a national collaboration involving National Jewish Medical and Research Center, Vanderbilt University School of Medicine, and University of Colorado, Boulder. The purpose of the collaboration is to determine if mycobacteria have a role in sarcoidosis immunopathogenesis. We will combine the sarcoidosis and control resources 1) to perform molecular characterization of sarcoidosis granulomas using genes which speciate pathogenic mycobacteria, 2) to compare T-cell specific interferon-y production to mycobacterial peptides in sarcoidosis patients to CBD patients, a PPD- control population, and patients with M. tuberculosis infection, 3) to use in situ hybridization to localize mycobacteria within sarcoidosis species in order to better understand host-pathogen interactions. These findings, which will assess in an independent and complementary fashion the role of mycobacteria in sarcoidosis immunopathogenesis, may have an impact on future therapeutic modalities for sarcoidosis.